1. Field of the Invention
The present invention relates to a warm air furnace having means for discharging drain which is a condensation of water vapor in combustion gas.
2. Description of the Related Art
Conventionally, as a drain discharging means in a warm air furnace, there is known a configuration formed so as to reduce the combustion gas combusted at the combusting means from leaking into a room. The first example has a drain pipe provided at a midstream of an exhaust passage with a sealed lower end, and a small-diameter hole formed at an upper side surface of the drain pipe (refer to Japanese utility model laid-open No. S57-010658). The second example has an orifice provided inside the drain pipe (refer to Japanese utility model laid-open No. S54-169937). The third example makes the inner diameter of a drain discharging pipe to be small diameter such that an exhaust gas does not leak because a surface tension of the drain (refer to Japanese utility model laid-open No. S53-145752).
In the drain discharging means of the warm air furnace as is mentioned above, in the first example, drain is accumulated in the drain pipe from the lower end of the drain pipe to the height of the hole at the side surface of the drain pipe. Further, in the second and third examples, because of the orifice provided in the drain pipe or because a membrane is generated at the lower end of the drain discharging pipe from the surface tension of the drain, drain is accumulated in the drain pipe or the drain discharging pipe until a head of water overcoming the surface tension of the drain is generated.
That is, there is a problem that drain is accumulated in the drain pipe of each of the conventional technique mentioned above, so that corrosion may occur at the drain pipe or the drain discharging pipe.